Heat treated and hardened article of manufacture made of fine grained deep hardened steels



i 7, 1 4 A. M. TALBOT EI'AL 2,279,079

HEAT TREATED AND HARDENED ARTICLE OF MANUFACTURE MADE OF FINE GRAINED DEEP HARDENED STEELS Fi led May 1, 1939 3 Sheets-Sheet l GRAIN SIZE RLUM I NUM PERCENTAGE INVENT R ALBERT MITRLBOQFS WILLIAM E. mEA Ns BY h ATTORNEY April 7, 1942- v A. M. TALBOT ET AL I 2,279,079

HEAT TREATED AND HARDENED ARTICLE OF MANUFACTURE STEELS MADE -OF FINE GRAINED DEEP, HARDENED :5 sheets-sheet 2 Filed May 1, "1.938

.SSSI' HLUM 1 NU N1 PERCENTAGE W\ m m WWUZDKiI JJMTZED FULL HARDENING INCREASE DUE TO CO-PRESEINCE' OF Si AND Al SLIGHT HARDENING TOTAL. ALLOY CONTENT lNVEN TORS ERT M. TALBOT YC. IY'I EA R NS ATTORNEY April 7, 1942.

BRINELL HARDNESS A, M. TALBOT ET AL 2,279,079

HEAT TREATED AND HARDENED ARTICLE OF MANUFACTURE Y MADE OF. FINE GRAINED DEEP HARDENED STEELS 4 Filed May 1, 1939 3 Sheets-Sheet 5 SILICON PERCENT-AGE V) V) LL! 2 o 0: t I

.1 J h] E 0: an

75% O I wo INCH DIAMETER INVENTORS ALBERT NLTALBOT WILLIANE C MEHRNS ATTORNEY Pate'n'ted Apr. 7, 1942 ACTURE- MADE OF FINE GRAINED nnsr HARDENED STEELS Albert M. Talbot, Fair Haven, and William 0.

Mearns, Elizabeth, N. J., assignor to The International Nickel Company, Inc.,

New YO Ik) "N. Y., a corporation of Delaware Application May 1, 1939, Serial No. 270,992 4'Claims. 1 (01. 148-31)- The present invention relates to heat treated and hardened articles of manufacture, and more particularly, to heat treated hardened steel articles of manufacture characterized by a fine grained and normal structure combined with deep hardness and high mechanical properties.

Until comparatively recent years it was the opinion of metallurgists that the physical and mechanical properties of steels and other alloys depended solely upon the chemical composition,- and that two samples of any metal or alloy having substantially the same chemical composition would exhibit the same properties under the same conditions. Almost two decades ago, however, it was observed in connection with the carburization of steel that anomalous results in hardening were obtained with steels, which results could not be explained on the basis of differences in amounts of the elements listed in the chemical specifications. McQuaid and Ehn (Transactions A. I. M. E., vol LXVII, 1922, pages 341 et seq.) observed that steels which hardened uniformly and deeply, and which they denoted normal,

' were coarse grained, whereas those which were not hardened, or which did not harden uniformly, which they denoted abnormal, were fine grained. By coarse and fine grained steels, they referred to the austenite grain size as obtained when heated at ordinary carburization temperatures, for example, when subjected to the present A. S. T. M. grain size test, and not to the size of the grains of the steel after cooling to room temperatures. Coarse and fine grained steels are' also defined as steels which have low and high coarsening temperatures. Under standard A. S. T. M. grain size test. conditions the steels will exhibit fine or coarse grains depending upon whether the coarsening temperature of the particular steel is aboveor below the temperature used in the test and upon the difference in temperature between the coarsening temperature and the test temperature. Subsequent investigation band of ferrite sometimes containing large spheroids of carbide. In an earlier article by Bain entitled. Factors affecting the inherent hardenability of steel appearing in Transactions A. S. S. T., vol. 20, 1932, pages 385 et seg., Bain stresses the fact that, other things being equal,

the fine grained austenite transforms more rapidly, appears more abnormal as cooled, and hardens less deeply than the coarse grained austenite. It follows, therefore, that fine grained steels are associated usually with abnormality and shallow hardenability, whereas coarse grained steels are associated with normal structure and deep hardenability for their alloy content.

The observation of the importance of grain.

size on the properties of steel naturally was followed by numerous attempts to explain .the reason for the difference in grain size, and by extensive search to develop methods for its control. It was found that the addition of certain amounts of aluminum yielded fine grained steel whereas the addition of lesser amounts yielded coarse grained steels. -However, the instructions proposed by the art for the control of grain size to produce fine or coarse grained steels could not be modified by selecting intermediate amounts of aluminum to produce an intermediate grain size. It was also recognized that as th silicon content of steel increased above the amount present in commercial steels, the steel tended to become coarser grained.

The problem 'of producing a fine grain deep hardening normal steel capable also of being heat treated to high hardness still confronted the art despite the numerous attempts which have been made to solve this baiiling and outstanding problem. f

Although many attempts have been made to remedy the aforementioned shortcomings, none 40 as far as we are aware, was entirely successful revealed notable diiferences in the metallurgical constitution of the normal and the abnormal steels. Davenport and Bain, in their article entitled General relations between grain size and hardenability and the normality of steels, published in Transactions A. S. M., vol. XXII, 1934, pages 879 et seq state that normal structure is characterized by thin, smooth, carbide envelopes entirely contiguous with the finer lamellar pearlite, and that abnormal structure is characterized by thick carbide envelopes with coarse lamellar pearlite, if any, separated from the network, which may be discontinuous, by a wide to when carried into practice. commercially.

We have discovered that the prior art shortcomings can be avoided and that new and unexpected results can be consistently obtained by incorporating critical and controlled amounts of aluminumand silicon together in steels.

It is an object of the present invention to provide improved heat treated and hardened articles of manufacture made of fine grained normal steels combining deep hardness with high tensile properties and ductility.

It is another object of the present invention to provide improved heat treated and deep hardened articles, of manufacture made of fine grained low alloyed steels having deep hardensilicon at various aluminum ability combined with physical. properties exceeding that of more highly alloyed and more expensive steels.

It is a further object of the present invention to provide heat treated and hardened steel articles ofmanufactur'e having a more controllable and predictable grain size.

The invention contemplates the production of heat treated and hardened articles of manufacture made of steels having improved deep hardenability combined with fine grain size, for example, about No. A. S. T. M. or smaller.

The invention also contemplates providing means for converting steels which would ordlnarily be coarse grained into'fine grained normal steels possessing deep hardening properties.

The invention further contemplates providing means for securing grain sizes within the range of No. 4 to No. 6 A. S. T M. which heretofore it has been very difiicult to obtain consistently.

Other objects of the invention will becomeapparent to those skilled in the art from the following description taken in conjunction with the accompanying drawings in which:

Fig. 1 is a graph illustrating the effect of aluminum upon the grain size of steel having a normal silicon content;

Fig. 2 is a graph showing the combined effect of aluminum and silicon on the grain size of a low alloyed steel;

Fig. 3 depicts a graph illustrating the combined effect of aluminum and silicon on the hardness of the same steel;

Fig. 4 is a graph illustrating the eiiect of aluminum and silicon together upon the hardenability of steel;

Fig. 5 is a series of curves depicting the effect of levels upon the hardenability of a low alloyed steel; and

Fig. 6 shows the depth hardening curves for a steel made in accordance with the present invention and a similar steel containing normal and usual amounts of aluminum and silicon.

We have made a surprising discovery that additional amounts of aluminum above the amounts normally used to control grain size, for

example about 0.03%, added to a well deoxidized melt result in the reversal of the aluminum efiect on grain size and produce coarsening in grain size, particularly when reaches habout 0.08%.. The effect. of aluminum will bereadily observed from Fig. l in which the aluminum content is plotted against the grain size of the steel. la men data illustrative of the reversal in: the aluminumefiect upon a steel of the S. A. E. 3045 type are included in Table 1:

I, Table 1 Chromium Carbon rain Sim Aluminum S. T M

Per cent Per cent Per cent Per cent 0 0 1 2 (l. 03 8 0. 04 7-8 0. 05 6 0.08 5 U. 30 4 the aluminum content refining, i. e., on the descending side of the curve,

small amounts of aluminum do not have the large effects on the grain size that is obtained upon the ascending side of the curve. Aluminum in excess of the amount necessary to produce maximum grain refinement affords greater accuracy in controlling and predicting grain size and for obtaining the desired intermediate grain sizes. Once maximum grain refinement has been reached; change in grain size is markedly slower and more predictable with the resulting wider control over grain size. We have made the further surprising and unexpected discovery that the co-presence of silicon in amounts larger than normal along with aluminum has a marked effect upon the slope of the descending side of the curve and a very strong beneficial effect upon the grain' size and the properties of the steel, including hardenability, tensile properties, ductility, impact, etc. Increased amounts of silicon decrease the slope of the curve shown in Fig. 1 on the descending side as well as raise the grain size number obtainable and permit more accurate control of the grain size. particularly in the more useiul intermediate grain sizes, than has been possible heretolore. Either silicon or aluminum used alone in sufficient quantity will produce a coarse grain steel whereas the use of the two elements together in amounts that would ordinarily cause grain coarsening if used singly surprisingly results invariably in a fine grain normal steel. When we refer in the specification and claims to fine grain, coarse grain, grain size," the- A. S. T. M. grain size number, etc., we mean the austenite grain size as determined under standard test conditions and not the actual grain size. As pointed out by Grossman (Trans. American Soc. for Metals; vol. 22, 1934, p. 861),

the austenite grain size is a record of the size of tions. Both grain size and normality or abnormality usually have been determined by microscopic examination of samples of steel after a specified carburizing cycle which usually would not be employed in commercial practice in ordinary hardening of steels and articles made there'- irom. The marked refining effects upon the grain size and thecontrol over grain size of copresent controlled amounts of aluminum and silicon is illustrated in Fig. 2 on S. A. E. 3045 steels. It will be noted from the curves that the reversal effect of aluminum is modified by the co-presence of silicon and that increasing amounts of silicon above normal amounts decrease the grain size for any given aluminum content and also markedly eliminate the possibility of obtaining deleterious coarse grains. Thus at the 0.55% silicon level the grain size is never coarser than about No. 6 (A. ,S. T. M.) or smaller whereas at the 0.30% silicon level the grain size may be as large as No. 5 or somewhat coarser. Furthermore, increasing amounts of silicon decrease the slcpe on the descending side of the curve and thereby greatly incr'ease the range of aluminum available for grain size control particularly at the lower aluminum levels where accurate control is most diflicult.

The relatively small combined amounts of ability of steel is illustrated in Fig. 3 in which j sections or smaller.

the surface hardnesses of S. A. E. 3045 steels are plotted against aluminum content for 2.75 inches sections of steels containing 0.30% and 0.55% silicon. It will be noted that the reversal eifect of aluminum is present in the hardness curves the steel at all values of aluminum. Similar ef-- fects are also obtained at the center of the sections as well as at the surface. Co-present amounts of aluminum and silicon have marked beneficial effects upon both grain size and hardenability and convert steels which would ordinarily be coarse grained into fine grained normal steels while at the same time greatly increasing the hardenability oi. the steels. The copresence of controlled amounts of aluminum and silicon effect a more marked increase in the hardenability and the mechanical properties of lower alloyed steels than when they are co-pres-' ent in highly alloyed intrinsically deep hardening steels. Fig. 4 is a graph showing the effect of co-present amounts of aluminum and silicon, in accordance with the present discovery, upon the hardenability of increasing alloyed steels; The

efiect of aluminum and silicon on 'hardeiiability is most pronounced upon steels of intermediate hardenability whereas the effect on grain size is present regardless of the alloyed content. A ver important advantage of the new combination of aluminum and silicon for securing deep hardening is that thi property is obtained at less cost than by any known alternative means. By hardenability we mean the ability of a steel to harden effectively upon rapidly cooling, e. g., oil quenching, throughout large sections such as two inch sections or larger to approach the hardness obtained in small sections such as one inch Hardenability is also defined as the ability of a steel to produce a high .istics. The hardened articles also possess markedly increased mechanical properties, including tensile properties, ductility, impact, etc. The pronounced improvement in hardenability is particularly evident in the steels of intermediate alloy content which would in the-absence of high silicon and aluminum possess mediocre hardenability. In accordance with the present invention the aluminum and silicon must be controlled within the ranges given in Table H:

Table II Element Percentage Mora than 0.05% but less than about 0.5%. More than 0.30% but less than about 0.7%.

Aluminum Silicon The aluminum amounts given herein are for soluble aluminum as distinguished from aluminum present as aluminum oxide (alumina) which frequently amounts to about 0.06% aluminum as aluminum oxide depending upon the state of deoxidation of the meltat the time of the aluminum addition. The carbon content will ordinarily range between about 0.35%and about 1% carbon. Steels for direct hardening will contain 0.35% to about, 0.7% carbon while carburizing steels made in accordance with the present invention although initially containing less than about 0.35% carbon will possessin the carburized condition high properties, including high hardness, at andnear the surface where these charwill raise theupper limit, whereas such elements as molybdenum and chromium will decrease the degree of surface and center hardness in large sections or as the ability of a steel to exhibit complete martensitization. deep hardenability is defined as the ,abihty of a steel to produce a high surface hardness, for example about 450 Brinell hardness, or higher combined with depth of penetration of that hardness or small change in hardness with penetration. or course, it will be understood that these characteristics refer to the as quenched-conditinguished from abnormality which was heretofore generally characteristic of fine grain aluminum-treated steels.

Broadly stated, the present invention provides improved heat treated and hardened articles of manufacture made of worked steel containing controlled and critical proportions of aluminum and silicon in amounts higher than ordinarily present in steel. The co-presence 01' aluminum and silicon imparts'to the hardened articles accurate grain size, for example, No. 5 (A. S. T. M.) or smaller, and normality to a high degree combinedwith improved deep hardening character- Deep hardening or acteristics are of controlling importance. The

.manga'ne'se content should be 'at least 0.4%, preferably higher, for example 0.8%. It will be understood that the upper and lower limits stated for silicon and aluminum will vary somewhat with the base composition of the steel and the size of the section. Increased amounts of nickel,

manganese and carbon, particularly the latter,

upper limit. These opposing effects are believed due to the fact that the first'group of elements tend to increase the austenite domain whereas the second group, like aluminum and silicon, de-

crease the austenite domain. To secure full hardening it is essential to so compose the steel hardening treatment. The present invention is I particularly applicable to alloy steels containing ly or in position will fail to harden in the center of a two inch round to about 500 Brinell hardness on ing treatment it is usually desirable but not nec- Element Percentage Nickel M uuguuusu (hromiuul .\iol.\-luluuuu1 Typical examples of the low alloy contents in steels which are markedly benefited by the pres- 1 ent invention are given in Table IV which also includes an illustrative example of carbon steels. It is to be noted that where a. blank appears in the table it indicates a commercial absence of the element in question but may be present in small amounts such as 0.01% or 0.001%.

It is understood that in the compositions specified herein, small amounts of minor elements and incidental elements such as sulfur, phosphorus, etc., may be included and when the phrase balance substantially iron or balance substantially all iron is used it is intended to include minor amounts of such elements which may find their way into the composition as a result of commercial steel making practice or which may be intentionally added in amounts and for the purposes for which such elements have sometimes been employed in ferrous alloy compositions.

In carrying the present invention into practice it is preferred to maintain the aluminum and silicon within the approximate ranges given in Table V. When high hardenability and mechanical properties are desired, for example in direct hardened wrought steel articles, it is also highly advantageous to maintain the carbon and manganese within the ranges given. I Excellent properties are obtained if in addition about 1% to 2.6% of alloying elements, for example, nickel and chromium, are also present:

Table V Element Percentage Aluminum l to 0.2. Silicon 4 to 0.0. (.arbou Manganese The present invention contemplates heat treated and hardened articles of manufacture made of wrought steels containing controlled amounts of soluble aluminum and silicon in excess of those 6 normally co-present. The fulbbenefits of the invention are only realized when the steels have been worked and are in the heat treated condition. When the term heat treated or heat treating is employed herein it is used in the ordinary sense, i. e., it indicates that the steel is heated to just above the critical range and rapidly cooled, for example \oil quenched, thereby hardening the steel but also includes austempering or the like. In addition to the quench- 0 usually tempered below about 900 F., for example 300 to 800 F.

We have found that accurate cdntrol of alu-' minum and silicon within the ranges specified herein is of great importance in obtaining the desired results. Below 0.1% soluble aluminum the total hardness and the hardenability of the steel is less marked and below about 0.05% soluble' aluminum abnormality usually results. Above about 0.2 soluble aluminum, further improvement in the properties becomes slightly less pronounced until at about 0.5% soluble aluminum the properties fall oflf again. Below about 0.20% silicon very little improvement in hardenability is obtained particularly for low aluminum contents. Some improvement is obtained by increasing the silicon to 0.25 or 0.27% but it is preferred that the silicon exceed about 0.30%. With 0.30% silicon there is a rather marked improvement in both hardenability and grain size while far better results are obtained with about 0.4% to about 0.6% silicon. Beyond about 0.7% silicon the hardenability is again reduced rapidly, especially if appreciable aluminum is present and carbon and manganese are low. It is to be observed again that the upper limits for aluminum and silicon depend upon the amount and kind of alin Table VI:

Table VI Steel Chro- Mauga- Car- Sili- Aluml- Grain No. Nmkel mium nose hon con num size Per- Per Per Per Per cent cent Per cent cent cent cent Steels containing aluminum and silicon in the amounts contemplated by the present invention also possess an excellent combination of tensile strength, hardness and ductility. Typical illustrative examples of the mechanical properties developed by the steels contemplated by the present invention are given in Table VII. The ten-' sile properties are for specimens from sections about 1.25 inches in diameter which are oil quenched from about 1525 F. followed by a draw at about 700 F.:

B. H. N. =Brinell hardness number.

'l. S. =Tensile strength in thousand pounds per sq. inch.

Y. P.=Yield point in thousand pounds per sq. inch.

P. L. Proportional limit 111 thousand pounds per sq. Inch.

';El.= Per cent elongation.

13R. A.= Per cent reduction in area.

lmpact= Charpy impact in loot-pounds.

Table VIII gives the mechanical properties of steel No. 27 and No. 28 drawn at 1000 F. in-

stead of at 700 F. as in Table VII:

Table VIII Steel B.H.N.' T.S. Y.P. P.L. %Ei.%R.A. Impact 25:1. 2%; i228 iii? i332 iii 52:3 it

See footnote Table VII for key.

Table IX shows the effect of section size (in inches) upon the mechanical properties of steel 'No. 16. The smaller size was oil quenched from l525 F. whereas the larger section was oil quenched from 1550 F. Both sections were then drawnat 700 F.

Table IX Size B.lI.N. T.S. Y.P. P.L. %El.%R.A. Impact 3515:; 213 i352 i513 58:3 iii? 23:5 15:;

See footnote Table VII for key. 5

Table X illustrates the deep hardening. qualities of the steels produced in accordance with the present invention. All specimens were 2 inch wrought sections quenched at 1550 F. (not drawn). The Brinell hardness values given are for the indicated distance from the center of the section: 1

I Table X B. N. at distance from center (inches) Steel No. I Center 31 $4 Surface At inches from center 0! section.

In Fig. 6 hardenability curves are plotted for two inch sections of steel No. 16 containing 0.44% silicon and 0.15% aluminum (curve A) and for a similar steel (0.5% nickel, 0.49% chromium, 0.77% manganese, and 0.41% carbon) containing normal amounts of aluminum and silicon,

i. e., 0.03% aluminum and 0.18% silicon (curve B). The improved hardenability and greater about 0.6%.

depth hardness or the improved steel over the ordinary steel is obvious.

. r The co-presence of aluminum and silicon withcontent steels which initially; have lower hardnesses The improvement in the low alloy nickel-chromium steels is particularly noticeable.

Increased silicon for a given aluminum content,

for example 0.06% or 0.1% aluminum, increases the depth hardening properties as distinguished from the shallow hardening characteristic 01 normal silicon and aluminum containing steels. The effectis particularly marked when silicon is at least about 0.4% S. A. E. 3050- steels containing aluminum and silicon are improved to such an extent that the properties exceed that of higher alloyed steels, e. g., S. A. E. 4140 steelsl S. A. E. 3140 steels produced in accordance with the present invention have hardenabilities' exceeding standards S. A. E. 4140, 4640 and4840 steels, and equal to that of standard 8. A E. 3340 steels, particularly in the larger sized sections.

The steels contemplated by the present invention may be produced in the customary manner used in good steel making practice. It is preferred but not necessary that the melt be completely deoxidizedwith a silicon-containing deoxidizer such as ferro-silicon or silicon-manganese just previous to the' alloy additions of aluminum and silicon to leave the required -mal steels and makes possible the use of these steels in a large number of applications which previously required more expensive steels. The present invention provides improved heat treated and hardened articles of manufacture made of worked steels characterized by deep hardening and a fine grained normal structure combined with a high combination of tensile strength and ductility. The articles of manufacture-provided I by the present invention are made of steels containing besides aluminum 0.5% to about 1.2%

and silicon as speci fled hereinbefore about 0.35% to about 1% carbon, about 0.4% up to 2% manganese, about 0.001% up to about 3.5% of metal from the group consisting of nickel, chromium and molybdenum, more than 0.05% and up to 0.5% aluminum, about 0.3% to about 0.7% silicon, and the balance, i. e., more than about of the steel, is iron. The invention is of particular benefit in heat treated and hardened articles of manufacture made of low alloy steels containing about 1% to 3% of combined manganese and metal. of the group consisting of nickel, chromium and molybdenum. Since at least about 0.4% will be manganese, up to about 2.6% of the total may be metal of the group consisting of nickel, chromium and molybdenum. Heat treated and hardened articles of manufacture made of steels containing about 0.4% to about 1.25% nickel, about 0.4% to 0.7% chromium, about manganese, and about 0.35%

. non-nitrided" article is referred to herein we do not intend to include such articles. Specific examples of improved heat treated and hardened articles include machine elements and other hardened parts which are used in the quenched or quenched and drawn condition, such as automotive and machine parts. Heat treated and hardened axles, shafts, crankshafts, connecting rods, king pins, transmission gears, pinions, ring gears, valves, springs, die blocks, dies, headers, piercers, die inserts and the like are typical examples of the hardened machine elements contemplated by the present invention.

Although the present, invention has been described in conjunction with preferred embodi ments, it is to be understood that modifications and variations may be resorted to Without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such variations and modifications are considered to be within the purview and scope of the appended claims.

We claim:

1. As a new article of manufacture, a nonnitrided, heat treated and hardened machine element made of wrought steel constituted of a deep hardened and fine grained to intermediate grained structure comprising about 0.35% to 0.65% carbon, 0.5% to 1.2% manganese, 0.4% to 1.25% nickel, 0.4% to 0.7% chromium, 0.1% to 0.2% aluminum, 0.4% to 0.6% silicon, and the balance substantially all iron, said machine element being characterized by a grain size at least as small as about No. 5 A. S. T'. M. and normality under standard test conditions combined with deep hardness and high mechanical properties.

2. As an article of manufacture, a non-nitrided, heat treated and hardened machine element made of wrought steel constituted of a deep hardened and fine grained to intermediate grained structure comprising about 0.35% to 0.65% carbon, 0.5% to 1.2% manganese, 0.4% to 1.25% nickel, 0.4% to 0.7% chromium, more than 0.05% and up to 0.5% aluminum, more than 0.3% and up to 0.7% silicon, and the balance substantially all iron, said machine element being characterized by a grain size of about No. 5 A. S. T. M. or. smaller and normality under standard test conditions combined with deep hardness and high mechanical properties.

3. A heat treated and hardened wrought article of manufacture made of non-nitrided steel constituted of a deep hardened and fine grained to intermediate grained structure comprising about 0.35%to 0.65% carbon. 0.5% to 1.2% manganese, 0.4% to 1.25% nickel, 0.4% to 0.7% chromium, 0.1% to about 0.2% aluminum, 0.4% to 0.6% silicon, and the balance substantially all iron, said article being characterized by a grain size at least as small as about No. 5 A. S. T. M.

and normality under standard test conditions combined with deep hardness and high mechanical properties.

4. A heat treated and hardened wrought article of manufacture made of non-nitrided nickel steel constituted of a deep hardenedand fine grained to intermediate grained structure comprising about 0.35% to 1% carbon, 0.4% to 2% manganese, 0.4% to 3.5%.nickel, 0.4% to 1.5% chromium, more than 0.05% and up to 0.5% aluminum, more than 0.3% and up to 0.7% silicon,

and the balance substantially all iron, said ar-' ticle being characterized by a grain size at least as small asabout No. 5 A. S. T. M. and normality 'under standard test conditions combined with deep hardness and high mechanical properties.

ALBERT M. TALBO I. WILLIAM C. MEARNS. 

